The disclosure relates generally to determining characteristics of solar cells, and in particular to determining a diffusion length and absorption coefficients of a thin-film solar cell.
Thin film solar cells, such as cadmium telluride (CdTe), Cu(In,Ga)Se2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are growing solar cell technologies compared to the dominant silicon solar cell technology due to their thin material requirements and large scale manufacturability. In thin film solar cells, an absorber layer is embedded within one or more buffer layers and anti-reflective layers and is sandwiched between conductive contacts.
Minority carrier diffusion length (Ld) is a fundamental device characteristic of solar cells, especially thin film solar cells, that directly impacts the device performance. Diffusion length describes how long photo-generated minority carriers can travel before they recombine. Diffusion length needs to be maximized in all solar cells to maximize the efficiency of the solar cells. Long Ld in high performance solar cells like silicon (with indirect band gap) can be measured using surface photovoltage techniques. However, for devices with short diffusion lengths like thin film solar cells (with direct band gap) there are no known easy techniques for measuring diffusion length. In addition, there are no known easy techniques for measuring an absorption coefficient (α) of an absorber layer of a thin-film solar cell, because measuring the diffusion length and absorption coefficient requires isolating characteristics of the embedded thin-film layer.